Monomer composition for synthesizing recycled plastics, its manufacturing method, and recycled plastics and molded articles using the same

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, which contains a high-purity aromatic diol compound recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles using the same.The present invention also relates to a monomer composition for synthesizing recycled plastics, which contains a highly-added by-product recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles using the same.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0122001, filed September 13, 2021, Korean Patent Application No. 10-2021-0122002, filed September 13, 2021, Korean Patent Application No. 10-2021-0122003, filed September 13, 2021, Korean Patent Application No. 10-2021-0122004, filed September 29, 2021, Korean Patent Application No. 10-2021-0128892, filed September 29, 2021, and Korean Patent Application No. 10-2021-0136153, filed October 13, 2021, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a monomer composition for synthesizing recycled plastics, which contains a high-purity aromatic diol compound recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles each using the same.

[0003] The present invention also relates to a monomer composition for synthesizing recycled plastics, which contains high-value-added by-products recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles using the same. [Background technology]

[0004] Polycarbonate is a thermoplastic polymer, a plastic having excellent properties such as excellent transparency, flexibility and relatively low production costs.

[0005] Although polycarbonate is widely used for a variety of purposes, environmental and health concerns have been continually raised regarding its disposal.

[0006] Currently, physical recycling methods are being used, but since this involves problems associated with quality degradation, research is being conducted into chemical recycling of polycarbonate.

[0007] Chemical decomposition of polycarbonate refers to the process of obtaining aromatic diol monomers (e.g., bisphenol A (BPA)) by decomposing polycarbonate, and then using these monomers in polymerization to obtain high-purity polycarbonate.

[0008] Representative examples of such chemical decomposition include pyrolysis, hydrolysis, and alcoholysis. Among these, the most common method is alcoholysis using a base catalyst, but methanolysis has the problem of using methanol, which is harmful to the human body, and ethanol requires high temperature and pressure conditions, resulting in a low yield.

[0009] In addition, an alcohol decomposition method using an organic catalyst is known, but the reality is that it has a drawback in terms of economics. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a monomer composition for synthesizing recycled plastics, which can ensure a high-purity aromatic diol compound recovered by recycling polycarbonate resins through chemical decomposition.

[0011] The present invention also provides a method for producing the monomer composition for synthesizing recycled plastics, and a recycled plastic and a molded article using the monomer composition for synthesizing recycled plastics. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a color coordinate L* of more than 95, and a color coordinate a* of -0.06 to 0.10, and is characterized in that the monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin.

[0013] The present invention also provides a monomer composition for synthesizing recycled plastics, comprising two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, the dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate being recovered from polycarbonate-based resins.

[0014] The present invention also provides a method for producing a monomer composition for synthesizing recycled plastics, the method comprising the steps of depolymerizing a polycarbonate-based resin in a solvent containing methanol and ethanol, and separating a carbonate precursor from the depolymerization reaction product.

[0015] The present invention also provides a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastics and a comonomer.

[0016] The present invention also provides a molded article comprising the recycled plastic.

[0017] Hereinafter, a monomer composition for synthesizing recycled plastics according to specific embodiments of the invention, a production method thereof, and recycled plastics and molded articles using the same will be described in more detail.

[0018] Unless otherwise expressly stated herein, the terminology used is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

[0019] As used herein, the singular forms "a," "an," and "the" include the plural forms as well, unless the context clearly indicates to the contrary.

[0020] As used herein, the meaning of "comprising" is to embody certain properties, regions, integers, steps, operations, elements, components and / or components, and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components and / or groups.

[0021] In this specification, terms including ordinal numbers such as "first" and "second" are used for the purpose of distinguishing one component from another component, and are not limited by the ordinal number. For example, within the scope of the present invention, a first component may be named a second component, and similarly, a second component may be named a first component.

[0022] 1. Monomer composition for synthesizing recycled plastics (1) First composition According to one embodiment of the present invention, there is provided a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a color coordinate L* of more than 95, and a color coordinate a* of -0.06 to 0.10, and is recovered from a polycarbonate resin.

[0023] The present inventors have confirmed through experiments that the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention satisfies the characteristics of high purity and excellent color coordinates like those of a newly synthesized aromatic diol compound, even though the monomer composition is recovered by recycling through chemical decomposition of polycarbonate-based resin, and therefore it is possible to realize excellent physical properties when synthesizing polycarbonate-based resin using the monomer composition, and thus completed the invention.

[0024] In particular, the monomer composition for synthesizing recycled plastics (first composition) of the one embodiment and the monomer composition for synthesizing recycled plastics (second composition) of the other embodiment, which contains two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and which are recovered from polycarbonate-based resin, are obtained simultaneously by a manufacturing method for a monomer composition for synthesizing recycled plastics described below.

[0025] In other words, the present invention has the technical advantage of being able to obtain a high-purity first composition containing an aromatic diol compound by recycling a polycarbonate-based resin through chemical decomposition, while at the same time obtaining a second composition containing two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which are high-added-value by-products.

[0026] Specifically, the monomer composition for synthesizing recycled plastics according to the embodiment is characterized in that it is recovered from a polycarbonate-based resin. That is, as a result of recovering from a polycarbonate-based resin in order to obtain the monomer composition for synthesizing recycled plastics according to the embodiment, a monomer composition for synthesizing recycled plastics containing an aromatic diol compound is also obtained.

[0027] The polycarbonate resin includes all homopolymers or copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers including aromatic diol compounds and carbonate precursors. When one type of carbonate repeating unit is contained, obtained by using only one type of aromatic diol compound and one type of carbonate precursor, a homopolymer can be synthesized. When one type of aromatic diol compound and two or more types of carbonate precursors are used as the monomers, or when two or more types of aromatic diol compounds and one type of carbonate precursor are used, or when two or more types of carbonates are contained by using one type of aromatic diol compound and one type of carbonate precursor as well as one or more other diols, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0028] In addition, the monomer composition (first composition) for synthesizing recycled plastics according to one embodiment may contain an aromatic diol compound. Specific examples of the aromatic diol compound include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol A), and bis(4-hydroxyphenyl)methane. Examples of the aromatic diol compound include bisphenol Z), 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, or a mixture of two or more of these. Preferably, the aromatic diol compound of the monomer composition (first composition) for synthesizing recycled plastics of the embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0029] The aromatic diol compound is characterized by being recovered from the polycarbonate-based resin used in recovering the monomer composition for synthesizing recycled plastics. That is, the aromatic diol compound is also obtained as a result of recovery from the polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when a new aromatic diol compound is added externally apart from the recovery from the polycarbonate-based resin to produce the monomer composition for synthesizing recycled plastics of the embodiment, it is not included in the category of the aromatic diol compound of the present invention.

[0030] Specifically, the term "recovered from the polycarbonate-based resin" means that the polycarbonate-based resin is obtained by a depolymerization reaction. The depolymerization reaction may be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction may be carried out under basic (alkaline) conditions. In particular, the depolymerization reaction is preferably carried out in a mixed solvent of ethanol and methanol, as described below.

[0031] Meanwhile, the monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate b* value of less than 2, or 0.1 or more, or 0.1 to 1.9, or 1.49 to 1.80. The monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate L* value of more than 95, or 100 or less, or more than 95 to 100, or 95.8 to 100, or 95.9 to 96.3. The monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate a* value of -0.06 to 0.10, or -0.05 to 0.10, or -0.04 to 0.09.

[0032] In the present invention, the term "color coordinates" refers to coordinates in the CIE Lab color space, which is a hue value defined by the CIE (Commission International de l'Eclairage), and any position in the CIE color space is expressed by three coordinate values: L*, a*, and b*.

[0033] Here, the L* value indicates brightness, with L* = 0 indicating black and L* = 100 indicating white. In addition, the a* value indicates whether the color having the corresponding color coordinates is biased toward pure red or pure green, and the b* value indicates whether the color having the corresponding color coordinates is biased toward pure yellow or pure blue.

[0034] Specifically, the a* value ranges from -a to +a. The maximum value of a* (a*max) indicates pure red, and the minimum value of a* (a*min) indicates pure green. The b* value ranges from -b to +b. The maximum value of b* (b*max) indicates pure yellow, and the minimum value of b* (b*min) indicates pure blue. For example, a negative b* value indicates a hue biased toward pure blue, and a positive b* value indicates a hue biased toward pure yellow. Comparing b*=50 and b*=80, this means that b*=80 is closer to pure yellow than b*=50.

[0035] When the color coordinate L* value of the monomer composition for synthesizing recycled plastics according to the embodiment is excessively decreased to 95 or less, the color characteristics of the monomer composition for synthesizing recycled plastics according to the embodiment become poor.

[0036] On the other hand, if the color coordinate a* value of the monomer composition for synthesizing recycled plastics of the embodiment is excessively increased to more than 0.10, the hue of the monomer composition for synthesizing recycled plastics of the embodiment is too red, resulting in poor color characteristics.

[0037] In addition, if the color coordinate a* value of the monomer composition for synthesizing recycled plastics of the embodiment is excessively decreased to less than −0.06, the hue of the monomer composition for synthesizing recycled plastics of the embodiment is too green, resulting in poor color characteristics.

[0038] The method for measuring the color coordinates L*, a*, and b* of the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and various methods for measuring color characteristics in the plastics field may be used without limitation.

[0039] However, as an example of a method for measuring the color coordinates L*, a*, and b* of the monomer composition for synthesizing recycled plastics according to the embodiment, the values ​​can be measured in reflection mode using a HunterLab UltraScan PRO Spectrophotometer.

[0040] Meanwhile, in the monomer composition for synthesizing recycled plastics of the embodiment, the purity of the aromatic diol compound may be more than 99%, or not more than 100%, or more than 99% and not more than 100%, or 99.1% to 100%, or 99.1% to 99.5%, or 99.1% to 99.4%.

[0041] The method for measuring the purity of the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and may be, for example, 1 H NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc. can be used without limitation. Specific methods, conditions, devices, etc. of the NMR, ICP-MS, HPLC, and UPLC can be various conventionally known methods, conditions, devices, etc. without limitation.

[0042] As an example of a method for measuring the purity of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to the embodiment, the monomer composition for synthesizing recycled plastics according to the embodiment was dissolved in acetonitrile (ACN) solvent at 1 wt % under normal pressure and 20 to 30° C., and the purity of bisphenol A (BPA) was analyzed using UPLC (ultra performance liquid chromatography) on a Waters HPLC system using an ACQUITY UPLC (registered trademark) BEH C18 1.7 μm (2.1*50 mm column).

[0043] In this way, in the monomer composition for synthesizing recycled plastics according to one embodiment, the purity of the aromatic diol compound, which is the main target material for recovery, is significantly increased to more than 99%, and other impurities are minimized, so that when polycarbonate-based resins are synthesized using this, excellent physical properties can be achieved.

[0044] Meanwhile, in the monomer composition for synthesizing recycled plastics of the embodiment, two or more or all three compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are obtained as by-products. That is, in the monomer composition for synthesizing recycled plastics of the embodiment, a two-kind mixture of dimethyl carbonate and diethyl carbonate, a two-kind mixture of dimethyl carbonate and ethyl methyl carbonate, a two-kind mixture of diethyl carbonate and ethyl methyl carbonate, or a three-kind mixture of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is obtained as a by-product.

[0045] The two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are characterized in that they are recovered from a polycarbonate-based resin used in the recovery of the monomer composition for synthesizing recycled plastics of the one embodiment.

[0046] That is, as a result of recovery from polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment, two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are also obtained. Therefore, when two or more compounds selected from the group consisting of new dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are added externally in addition to recovery from polycarbonate-based resin to produce the monomer composition for synthesizing recycled plastics of the embodiment, they are not included in the category of two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate of the embodiment.

[0047] Specifically, the term "recovered from the polycarbonate-based resin" means that the polycarbonate-based resin is obtained by a depolymerization reaction. The depolymerization reaction may be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction may be carried out under basic (alkaline) conditions. In particular, the depolymerization reaction is preferably carried out in a mixed solvent of ethanol and methanol, as described below.

[0048] In the monomer composition for synthesizing recycled plastics in one embodiment, the main target substance for recovery is an aromatic diol compound, so two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are separately separated as by-products.

[0049] The monomer composition for synthesizing recycled plastics in the above-mentioned other embodiment corresponds to a separately separated by-product composition.

[0050] The monomer composition for synthesizing recycled plastics according to one embodiment can be used as a raw material for producing various recycled plastics (e.g., polycarbonate (PC)) as described below.

[0051] The monomer composition for synthesizing recycled plastics (first composition) of one embodiment may further contain a small amount of other additives and solvents. The specific types of additives and solvents are not particularly limited, and various substances that are widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate-based resins can be used without limitation.

[0052] The monomer composition for synthesizing recycled plastics (first composition) of the embodiment may be obtained by a method for producing a monomer composition for synthesizing recycled plastics, which will be described later. That is, the monomer composition for synthesizing recycled plastics (first composition) of the embodiment corresponds to a resultant product obtained through various filtration, purification, washing, and drying processes in order to obtain only aromatic diol compounds, which are the main target substances for recovery, in high purity after the depolymerization reaction of polycarbonate-based resin.

[0053] (2) Second composition Meanwhile, according to another embodiment of the present invention, there is provided a monomer composition for synthesizing recycled plastics, comprising two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, wherein the dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are recovered from polycarbonate-based resins.

[0054] The inventors have experimentally confirmed that the monomer composition for synthesizing recycled plastics (second composition) of the other embodiment can produce monomers with high added value by recycling polycarbonate-based resin through chemical decomposition to recover two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and have completed the invention.

[0055] The monomer composition for synthesizing recycled plastics according to another embodiment may further include two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, or all three compounds.

[0056] That is, the monomer composition for synthesizing recycled plastics of the other embodiment may further include a two-type mixture of dimethyl carbonate and diethyl carbonate, a two-type mixture of dimethyl carbonate and ethyl methyl carbonate, a two-type mixture of diethyl carbonate and ethyl methyl carbonate, or a three-type mixture of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0057] The two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are characterized in that they are recovered from a polycarbonate-based resin used in the recovery of the monomer composition for synthesizing recycled plastics of the one embodiment.

[0058] That is, as a result of recovery from polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the other embodiment, two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are also obtained. Therefore, when two or more compounds selected from the group consisting of new dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are added externally in addition to recovery from polycarbonate-based resin to produce the monomer composition for synthesizing recycled plastics of the other embodiment, they are not included in the category of two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate of the other embodiment.

[0059] Specifically, the term "recovered from a polycarbonate-based resin" means that the polycarbonate-based resin is obtained by depolymerization of the polycarbonate-based resin. The depolymerization may be carried out under acidic, neutral or basic conditions, and particularly under basic (alkaline) conditions.

[0060] The monomer composition for synthesizing recycled plastics in the other embodiment contains the dimethyl carbonate in a ratio of 1% to 30%, or 3% to 25%, diethyl carbonate in a ratio of 10% to 65%, or 16% to 60%, and ethyl methyl carbonate in a ratio of 30% to 60%, or 37% to 57%.

[0061] The method for measuring the ratio of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is not particularly limited, but an example is gas chromatography (GC) analysis. More specifically, the peak area value of each standard sample of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) dissolved in EtOH solvent at the same concentration and measured by GC is used as the reference value, and the ratio of the peak area value of each carbonate by-product (diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC)) in the sample (peak area value of sample / peak area value of standard sample) is obtained, and the total of the ratio of the peak area value of each carbonate by-product (diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC)) obtained by the GC result is 100%, and the relative ratio of each carbonate by-product can be calculated.

[0062] As described above, in the monomer composition for synthesizing recycled plastics according to another embodiment, ethyl methyl carbonate having high added value is contained in an excess amount, which can be utilized to recycle in various processes.

[0063] The monomer composition for synthesizing recycled plastics according to another embodiment can be used as a raw material for producing various recycled plastics (e.g., polycarbonate (PC), polyurethane, and epoxy resin) described below.

[0064] The monomer composition for synthesizing recycled plastics (second composition) of another embodiment may further contain a small amount of other additives and solvents. The specific types of additives and solvents are not particularly limited, and various substances widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate-based resins can be used without limitation.

[0065] The monomer composition for synthesizing recycled plastics (second composition) of the other embodiment may be obtained by a method for producing a monomer composition for synthesizing recycled plastics described below. That is, the monomer composition for synthesizing recycled plastics (second composition) of the other embodiment corresponds to a resultant product obtained through various filtration, purification, washing, and drying processes in order to obtain only dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate, which are the main target substances for recovery, in high purity after the depolymerization reaction of polycarbonate-based resin.

[0066] 2. Manufacturing method of monomer composition for synthesizing recycled plastics According to another embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin in a solvent containing methanol and ethanol; and separating a carbonate precursor from the depolymerization reaction product.

[0067] The present inventors have confirmed through experiments that, as in the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment, when a depolymerization reaction is performed to recycle a polycarbonate-based resin by chemical decomposition, alcoholysis is performed using both methanol and ethanol as reaction solvents, which not only ensures high purity of an aromatic diol compound, which is the main synthetic target substance in the present invention, but also ensures two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which are high addition by-products, thereby completing the invention.

[0068] In particular, when alcoholysis is performed using only methanol or only ethanol as in the conventional method, it is difficult to obtain ethyl methyl carbonate as a by-product, and it is difficult to obtain dimethyl carbonate and diethyl carbonate as by-products at the same time. However, according to the method for producing a monomer composition for synthesizing recycled plastics of another embodiment of the present invention, the aromatic diol compound, which is the main product, has high purity and excellent optical properties equivalent to or higher than those of the conventional method, and has the advantage that two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which have high added value, especially ethyl methyl carbonate, can be obtained in high yield.

[0069] Specifically, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of depolymerizing a polycarbonate-based resin in a solvent containing methanol and ethanol.

[0070] The polycarbonate resin includes both homopolymers and copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. When one type of carbonate repeating unit is contained, obtained by using only one type of aromatic diol compound and one type of carbonate precursor, a homopolymer can be synthesized. In addition, when one type of aromatic diol compound and two or more types of carbonate precursors are used as the monomers, or when two or more types of aromatic diol compounds and one type of carbonate precursor are used, or when one type of aromatic diol compound and one type of carbonate precursor are used and one or more types of other diols are used, a copolymer can be synthesized. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0071] The polycarbonate-based resin may be applied regardless of various forms and types, such as a new polycarbonate-based resin produced by synthesis, a recycled polycarbonate-based resin produced by a recycling process, or a polycarbonate-based resin waste.

[0072] However, if necessary, a pretreatment process of the polycarbonate resin may be performed before the depolymerization reaction of the polycarbonate resin to increase the efficiency of the process of recovering the aromatic diol compound and the carbonate precursor from the polycarbonate resin. Examples of the pretreatment process include washing, drying, pulverization, and glycol decomposition, and the specific method of each pretreatment process is not limited, and various methods widely used in the process of recovering the aromatic diol compound and the carbonate precursor by depolymerization of the polycarbonate resin may be applied without limitation.

[0073] The depolymerization reaction of the polycarbonate resin may be carried out under acidic, neutral, or basic conditions, and may be carried out under basic (alkaline) conditions. The type of base is not particularly limited, and examples include sodium hydroxide (NaOH) and potassium hydroxide (KOH). The base is a base catalyst that acts as a catalyst, and has the advantage of being more economical than organic catalysts that are mainly used under mild conditions.

[0074] The depolymerization reaction of the polycarbonate-based resin can be carried out by reacting the base with a content of 0.5 mol or less, or 0.4 mol or less, or 0.3 mol or less, or 0.1 mol or more, or 0.2 mol or more, or 0.1 mol to 0.5 mol, or 0.1 mol to 0.4 mol, or 0.1 mol to 0.3 mol, or 0.2 mol to 0.5 mol, or 0.2 mol to 0.4 mol, or 0.2 mol to 0.3 mol, relative to 1 mol of the polycarbonate-based resin. If the base is reacted with more than 0.5 mol relative to 1 mol of the polycarbonate-based resin, impurities increase due to the effect of an increase in the amount of alkaline salt generated, which reduces the purity of the target recovered material, and there is a limit to the reduction in the economic efficiency of the catalytic reaction.

[0075] The depolymerization reaction of the polycarbonate resin can be carried out in a solvent containing methanol and ethanol. The present invention has the advantage that the polycarbonate resin can be decomposed in a solvent containing methanol and ethanol to stably obtain bisphenol A, which is a high-purity monomer, and two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which have high added value, can be further obtained as reaction by-products.

[0076] Specifically, ethanol may be contained in an amount of 1 to 15 moles, or 1.1 to 15 moles, or 1.2 to 15 moles, or 1.1 to 10 moles, or 1.2 to 10 moles, per mole of methanol. If ethanol is used in an amount that is too small, such as less than 1 mole, less than 1.1 moles, or less than 1.2 moles, per mole of methanol, there is a problem that the content of methanol, which is harmful to the human body, increases excessively. In addition, if ethanol is used in an amount that is too large, such as more than 15 moles, per mole of methanol, there is a limit in that it is difficult to sufficiently secure dimethyl carbonate or ethyl methyl carbonate as a by-product due to the reduced methanol content.

[0077] The content of the methanol and ethanol may be 5 to 15 moles, or 8 to 13 moles, or 10 to 12 moles, per mole of the polycarbonate resin. The content of the methanol and ethanol means the sum of the content of the methanol and the content of the ethanol. In addition, since methanol and ethanol have good solubility in bisphenol A, the above-mentioned range of methanol and ethanol must be included. If the content of the methanol and ethanol is excessively reduced to less than 5 moles per mole of the polycarbonate resin, the alcoholysis of the polycarbonate resin is difficult to proceed sufficiently. On the other hand, if the content of the methanol and ethanol is excessively increased to more than 15 moles per mole of the polycarbonate resin, the economic efficiency of the process is reduced due to the excessive use of alcohol.

[0078] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may further include, in addition to methanol and ethanol, one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0079] The organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0080] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent to be mixed with methanol and ethanol, there is an advantage that the dissolving property for polycarbonate is improved and the reactivity is improved.

[0081] The content of the organic solvent may be 16 to 20 moles, or 16 to 18 moles, per mole of the polycarbonate resin. The content of the organic solvent may be 1.5 to 2 moles per mole of the total of methanol and ethanol. By mixing the polycarbonate resin, methanol, ethanol, and the organic solvent within the above range, it is advantageous that a required level of depolymerization reaction of the polymer can be performed.

[0082] The temperature for carrying out the depolymerization reaction of the polycarbonate-based resin is not particularly limited, and may be, for example, 20° C. to 100° C., or 50° C. to 70° C. The time for carrying out the depolymerization reaction of the polycarbonate-based resin is 1 hour to 30 hours, or 4 hours to 6 hours.

[0083] Specifically, the above conditions are milder process conditions than the conventional pressurized / high temperature process, and stirring under the above conditions allows the process to be carried out under milder conditions than the conventional pressurized / high temperature process. In particular, stirring at 50°C to 70°C for 4 to 6 hours has the advantage of being able to obtain the most efficient results in terms of reproducibility and stability.

[0084] That is, the present invention has an advantage that a high purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using an organic catalyst and without using a pressurized / high temperature process by adjusting the type and amount of the mixed solvent and the type and content of the base catalyst, and that diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate can be obtained as by-products because methanol and ethanol solvents are used.

[0085] More specifically, the step of depolymerizing the polycarbonate-based resin in a solvent containing methanol and ethanol may include a first step of preparing a catalyst solution by adding a base to a mixed solvent of methanol and ethanol and an organic solvent, and a second step of adding a carbonate-based resin to the catalyst solution and stirring the mixture. The details regarding the methanol, ethanol, organic solvent, base, and polycarbonate-based resin in the first step are as described above.

[0086] In addition, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of neutralizing the depolymerization reaction product with an acid before a step of separating a carbonate precursor from the depolymerization reaction product.

[0087] For example, the alkaline decomposition product of the polycarbonate resin contains an aromatic diol compound or a salt thereof, and since the main target material for recovery in the present invention is an aromatic diol compound, the salt of the aromatic diol compound obtained by the alkaline decomposition can be converted to the aromatic diol compound by an additional neutralization process with an acid. That is, when the depolymerization reaction of the polycarbonate resin is an alkaline decomposition, a neutralization reaction step with an acid can be performed.

[0088] The acid used in the neutralization reaction may be a strong acid, such as hydrochloric acid (HCl). The neutralization reaction using the strong acid may satisfy a pH of less than 6, or 4 or less, or 2 or less at the end of the neutralization reaction. The temperature during the neutralization reaction may be adjusted to 25°C or more and 100°C or less.

[0089] In addition, if necessary, after the neutralization step of the depolymerization reaction product with an acid, a process of removing remaining impurities by filtration or adsorption can be further performed. Specifically, the aqueous layer and the organic layer can be separated, and the organic layer can be filtered by vacuum filtration to recover a liquid containing the aromatic diol compound.

[0090] In addition, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of separating a carbonate precursor from the depolymerization reaction product. The separated carbonate precursor corresponds to the second composition in the embodiment. Thus, the separated carbonate precursor may include two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0091] For example, the depolymerization reaction product of the polycarbonate resin includes an aromatic diol compound or a salt thereof and a carbonate precursor. The content related to the aromatic diol compound and the carbonate precursor includes all of the content described above in the embodiment.

[0092] The step of separating the carbonate precursor from the depolymerization reaction product may include a step of vacuum distillation of the depolymerization reaction product. Although the conditions of the vacuum distillation are not particularly limited, in a specific example, the polycarbonate-based resin may be subjected to low-temperature distillation by pressurizing the depolymerization reaction product under conditions of a pressure of 200 mbar to 300 mbar and a temperature of 20°C to 30°C, and then reducing the pressure under conditions of a pressure of 10 mbar to 50 mbar and a temperature of 20°C to 30°C.

[0093] The separated carbonate precursor may be recycled without a separate separation and purification process, or may be recycled after, as necessary, conventional separation and purification such as extraction, adsorption, drying, etc. Specific purification conditions are not particularly limited, and various known purification techniques may be applied to specific purification devices and methods without limitation.

[0094] In addition, the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment may further include a purification step of the depolymerization reaction product from which the carbonate precursor is separated, thereby obtaining an aromatic diol compound, which is a main recovered material, and corresponds to the first composition in the embodiment.

[0095] Specifically, the purification step of the depolymerization reaction product from which the carbonate precursor is separated may include a washing step of the depolymerization reaction product from which the carbonate precursor is separated. Also, the purification step of the depolymerization reaction product from which the carbonate precursor is separated may include an adsorption purification step of the depolymerization reaction product from which the carbonate precursor is separated. Also, the purification step of the depolymerization reaction product from which the carbonate precursor is separated may include a recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated.

[0096] The order of the washing step, the adsorption purification step, and the recrystallization step is not particularly limited and may be any order, but for example, the washing step, the adsorption purification step, and the recrystallization step may be performed in that order. The washing step, the adsorption purification step, and the recrystallization step may each be repeated at least once. Specific apparatuses and methods for washing, adsorption, and recrystallization may be applied to various known purification techniques without any restrictions.

[0097] Specifically, in a step of washing the depolymerization reaction product from which the carbonate precursor is separated, the depolymerization reaction product from which the carbonate precursor is separated may contain an aromatic diol compound. However, since various impurities remain during a recovery process for obtaining an aromatic diol compound, washing may be performed to sufficiently remove the impurities to obtain a high-purity aromatic diol compound.

[0098] Specifically, the cleaning step may include a step of cleaning with a solvent at a temperature of 10° C. to 30° C., or 20° C. to 30° C., and a step of cleaning with a solvent at a temperature of 40° C. to 80° C., or 40° C. to 60° C., or 45° C. to 55° C. The temperature condition refers to the temperature inside a cleaning vessel where cleaning with a solvent is performed, and various heating mechanisms may be applied without limitation to maintain a high temperature that is higher than room temperature.

[0099] The washing step may be performed by first washing with a solvent at a temperature of 10° C. to 30° C. and then washing with a solvent at a temperature of 40° C. to 80° C. Alternatively, the washing step may be performed by first washing with a solvent at a temperature of 40° C. to 80° C. and then washing with a solvent at a temperature of 10° C. to 30° C.

[0100] More preferably, the washing step may be performed by first washing with a solvent at a temperature of 10° C. to 30° C., and then washing with a solvent at a temperature of 40° C. to 80° C., thereby minimizing corrosion of the reactor due to strong acid after the neutralization step.

[0101] The step of washing with a solvent at a temperature of 10° C. to 30° C. and the step of washing with a solvent at a temperature of 40° C. to 80° C. may each be repeated at least once.

[0102] In addition, if necessary, after the step of washing with a solvent at a temperature of 10° C. to 30° C. and the step of washing with a solvent at a temperature of 40° C. to 80° C., a step of removing the remaining solvent by filtration can be further performed.

[0103] More specifically, the difference between the temperature in the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature in the step of washing with a solvent at a temperature of 10°C to 30°C may be 20°C to 50°C.

[0104] The difference between the temperature in the step of washing with a solvent at a temperature of 40° C. to 80° C. and the temperature in the step of washing with a solvent at a temperature of 10° C. to 30° C. means a value obtained by subtracting the temperature in the step of washing with a solvent at a temperature of 10° C. to 30° C. from the temperature in the step of washing with a solvent at a temperature of 40° C. to 80° C.

[0105] If the difference between the temperature in the step of washing with a solvent at a temperature of 40° C. to 80° C. and the temperature in the step of washing with a solvent at a temperature of 10° C. to 30° C. is too low, such as less than 20° C., it is difficult to sufficiently remove impurities.

[0106] If the difference in temperature between the step of washing with a solvent at a temperature of 40° C. to 80° C. and the step of washing with a solvent at a temperature of 10° C. to 30° C. is excessively increased to more than 50° C., harsh conditions are formed in order to maintain the extreme temperature conditions, and the efficiency of the process is reduced.

[0107] The solvent used in the washing step may include one of water, alcohol, and organic solvents, such as tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0108] The solvent used in the washing step may be used in a ratio of 1 to 30 moles, or 2 to 25 moles, based on 1 mole of the polycarbonate resin used in the depolymerization reaction.

[0109] More specifically, the solvent in the step of washing with a solvent at a temperature of 10° C. to 30° C. may be an organic solvent. As the organic solvent, methylene chloride may be preferably used. In this case, the organic solvent may be used in an amount of 1 to 10 mol, or 1 to 5 mol, based on 1 mol of the polycarbonate resin.

[0110] The solvent used in the step of washing with a solvent at a temperature of 40° C. to 80° C. may be water. When water is used, residual salt-type impurities can be effectively removed. In this case, the solvent may be used in an amount of 20 to 30 mol, or 20 to 25 mol, based on 1 mol of the polycarbonate resin.

[0111] Meanwhile, in the adsorption purification step of the depolymerization reaction product from which the carbonate precursor is separated, an adsorbent may be contacted with the depolymerization reaction product. Examples of the adsorbent include activated carbon, charcoal, celite, or a mixture thereof. That is, the adsorption purification step of the depolymerization reaction product from which the carbonate precursor is separated may include a step of introducing an adsorbent into the depolymerization reaction product from which the carbonate precursor is separated, adsorbing and purifying the product, and then removing the adsorbent.

[0112] The activated carbon is a black carbon material having fine pores produced by subjecting a raw material to a carbonization process at about 500°C and an activation process at about 900°C. Examples of the activated carbon are not particularly limited, and various activated carbons such as plant-based, coal-based, petroleum-based, and waste-based activated carbons can be used without restriction depending on the type of raw material. More specific examples of the activated carbon include coconut shell activated carbon, wood activated carbon, and sawdust activated carbon as plant-based activated carbon. Also, examples of the activated carbon based on coal include lignite activated carbon, bituminous activated carbon, and anthracite activated carbon. Also, examples of the activated carbon based on petroleum include petroleum coke activated carbon and oil carbon activated carbon. Also, examples of the activated carbon based on waste include synthetic resin activated carbon and pulp activated carbon.

[0113] The conditions for adsorption purification using the first adsorbent are not particularly limited, and various conventionally known adsorption purification conditions can be used without limitation. However, as an example, the amount of adsorbent added is 40% by weight to 60% by weight relative to the polycarbonate resin, the adsorption time is 1 hour to 5 hours, and the adsorption method is stirring adsorption or a lab adsorption tower.

[0114] If necessary, the method may further include a step of adding a solvent to the depolymerization reaction product from which the carbonate precursor has been separated, prior to the adsorption purification step of the depolymerization reaction product from which the carbonate precursor has been separated. An example of the solvent is ethanol, and the ethanol may be added in a ratio of 1 to 20 mol, 10 to 20 mol, or 15 to 20 mol per mol of the polycarbonate resin. By adding a solvent to the depolymerization reaction product from which the carbonate precursor has been separated, the crystals of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor has been separated are redissolved in the solvent.

[0115] Meanwhile, in the recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated, various impurities contained in the depolymerization reaction product from which the carbonate precursor is separated can be sufficiently removed to obtain a high-purity aromatic diol compound.

[0116] Specifically, the recrystallization step may include a step of adding water to the depolymerization reaction product from which the carbonate precursor is separated to perform recrystallization. By performing the step of adding water to the depolymerization reaction product from which the carbonate precursor is separated to perform recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, so that impurities present in the crystals or between the crystals can be dissolved in the solvent to the maximum extent, and since the dissolved aromatic diol compound has poor solubility compared to the impurities, when the temperature is subsequently lowered, the aromatic diol compound is easily precipitated as crystals due to the difference in solubility.

[0117] More specifically, in the step of adding water to the depolymerization reaction product from which the carbonate precursor is separated to recrystallize, 200 to 400 mols or 250 to 350 mols of water can be used per mol of polycarbonate-based resin. If the amount of water used is too small, the temperature for dissolving the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor is separated becomes too high, resulting in poor process efficiency and making it difficult to remove impurities by recrystallization. On the other hand, if an excessive amount of water is used, the solubility of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor is separated becomes too high, resulting in a reduced yield of the aromatic diol compound recovered after recrystallization, and a reduced process efficiency due to the use of a large amount of solvent.

[0118] If necessary, after the depolymerization reaction product from which the carbonate precursor has been separated is recrystallized, a process of removing remaining impurities by filtration or adsorption may be further performed.

[0119] If necessary, a drying step may be further included after the recrystallization step. The residual solvent can be removed by the drying, and the specific drying conditions are not particularly limited, but the drying can be performed at a temperature of, for example, 10° C. to 100° C., or 10° C. to 50° C. Regarding the specific drying device and method used in the drying, various known drying techniques can be applied without any restrictions.

[0120] 3. Recycled plastics According to yet another embodiment of the present invention, a recycled plastic can be provided that includes the monomer composition for synthesizing recycled plastics (first composition) of the one embodiment and a reaction product of a comonomer. Also, a recycled plastic can be provided that includes the monomer composition for synthesizing recycled plastics (second composition) of the other embodiment and a reaction product of a comonomer.

[0121] The content relating to the monomer composition for synthesizing recycled plastics (first composition) of the one embodiment and the monomer composition for synthesizing recycled plastics (second composition) of another embodiment includes all of the content described above in the above embodiments.

[0122] Examples of the recycled plastic are not particularly limited, and include polycarbonate-based resins, polyurethane-based resins, epoxy resins, etc. Specifically, the recycled plastic including the monomer composition for synthesizing recycled plastics (first composition) of the embodiment and the reaction product of a comonomer can be applied to various plastics synthesized using an aromatic diol compound such as bisphenol A as a monomer without limitation, and a more specific example is polycarbonate-based resin.

[0123] In particular, the recycled plastic including the reaction product of the monomer composition for synthesizing recycled plastics (second composition) and comonomer of the other embodiment can be applied to various plastics synthesized using carbonate precursors such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate as monomers without restriction, and more specific examples include polycarbonate-based resins, polyurethane-based resins, and epoxy resins.

[0124] In particular, the polycarbonate-based resin includes all homopolymers or copolymers containing polycarbonate repeating units, and is a collective term for reaction products obtained by polymerization or copolymerization of monomers including aromatic diol compounds and carbonate precursors. When one type of carbonate repeating unit is contained, obtained by using only one type of aromatic diol compound and one type of carbonate precursor, a homopolymer is synthesized. When one type of aromatic diol compound and two or more types of carbonate precursors are used as the monomers, or when two or more types of carbonates are contained by using one type of aromatic diol compound and one type of carbonate precursor, or when two or more types of diols are used in addition to one type of aromatic diol compound and one type of carbonate precursor, a copolymer is synthesized. The homopolymer or copolymer may include all low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0125] More specifically, in the recycled plastics comprising the reaction product of the monomer composition for synthesizing recycled plastics (first composition) of the one embodiment and a comonomer, a carbonate precursor can be used as the comonomer. Specific examples of the carbonate precursor include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate, or bishaloformate. The monomer composition for synthesizing recycled plastics (second composition) comprising two or more compounds selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate of the other embodiment can also be used as the carbonate precursor.

[0126] In addition, in the recycled plastics containing the reaction product of the monomer composition for synthesizing recycled plastics (second composition) of the other embodiment and a comonomer, the comonomer may be an aromatic diol compound.

[0127] Specific examples of the aromatic diol compound include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol A), and bis(4-hydroxyphenyl)cyclohexane (bisphenol B). Examples of the aromatic diol compound include 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, and mixtures of two or more of these. The aromatic diol compound may be a monomer composition (first composition) for synthesizing recycled plastics, which contains the aromatic diol compound of the embodiment.

[0128] The reaction process of the monomer composition and the comonomer for synthesizing recycled plastics to synthesize the polycarbonate-based resin is not particularly limited, and various conventionally known methods for producing polycarbonate can be applied without any restrictions.

[0129] However, as an example of the method for producing the polycarbonate, a method for producing the polycarbonate may be used that includes a step of polymerizing a composition containing a monomer composition for synthesizing recycled plastics and a comonomer. In this case, the polymerization may be performed by interfacial polymerization, which allows the polymerization reaction at normal pressure and low temperature, and allows easy molecular weight control.

[0130] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. The pH during the reaction may be maintained at 9 or more or 11 or more.

[0131] The solvent that can be used in the polymerization is not particularly limited as long as it is a solvent that is used in the polymerization of polycarbonates in the art. For example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0132] The polymerization can be carried out in the presence of an acid binder, and as the acid binder, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine can be used.

[0133] In addition, the polymerization can be carried out in the presence of a molecular weight regulator in order to regulate the molecular weight of the polycarbonate during the polymerization. As the molecular weight regulator, an alkylphenol having 1 to 20 carbon atoms can be used, and specific examples thereof include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, or triacontylphenol. The molecular weight regulator can be added before the start of polymerization, during the start of polymerization, or after the start of polymerization. The molecular weight regulator can be used in an amount of 0.01 to 10 parts by weight, or 0.1 to 6 parts by weight, relative to 100 parts by weight of the aromatic diol compound, and a desired molecular weight can be obtained within the above range.

[0134] In addition, in order to accelerate the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound, or a quaternary phosphonium compound, such as triethylamine, tetra-n-butylammonium bromide, or tetra-n-butylphosphonium bromide, may be further used.

[0135] 4. Molded products According to yet another embodiment of the present invention, there is provided a molded product containing the recycled plastic of the other embodiment. The content related to the recycled plastic includes all of the content described above in the other embodiment.

[0136] The molded product may be obtained by subjecting the recycled plastic to various known plastic molding methods without limitation, and examples of the molding methods include injection molding, foam injection molding, blow molding, and extrusion molding.

[0137] The molded article is not particularly limited, and may be applied to various molded articles using plastics without any restrictions, such as automobile parts, electric and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, etc.

[0138] In addition to the recycled plastic of the other embodiment, the molded article may further contain, as necessary, one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent brighteners, ultraviolet absorbers, pigments, and dyes.

[0139] As an example of a method for manufacturing the molded product, the method may include thoroughly mixing the recycled plastic of the other embodiment and an additive using a mixer, extruding the mixture in an extruder to prepare pellets, drying the pellets, and then injecting the pellets into an injection molding machine. Effect of the Invention

[0140] According to the present invention, it is possible to provide a monomer composition for synthesizing recycled plastics, which contains a high-purity aromatic diol compound recovered by recycling through chemical decomposition of polycarbonate-based resins, a method for producing the same, and recycled plastics and molded articles using the same. It is also possible to provide a monomer composition for synthesizing recycled plastics, which contains a highly-added by-product recovered by recycling through chemical decomposition of polycarbonate-based resins, a method for producing the same, and recycled plastics and molded articles using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0141] The present invention will be described in detail below with reference to examples. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0142] <Example: Production of recycled bisphenol A monomer composition> Example 1 (1. Decomposition step) 28 mol of ethanol / methanol / methylene chloride mixed solvent (ethanol:methanol:methylene chloride=10:1:17 molar ratio) and 0.25 mol of sodium hydroxide were added to a 250 ml 3-neck flask and stirred. Then, 1 mol of waste polycarbonate (PC) was added and stirred at 60°C for 6 hours to carry out PC depolymerization. The product of the depolymerization reaction was cooled to room temperature to obtain a bisphenol A mixed solution.

[0143] (2. Neutralization Step) The mixture containing bisphenol A was neutralized at 20 to 30° C. using 0.25 mol of 1N hydrochloric acid (HCl), and then the aqueous layer and the organic layer were separated. The organic layer was filtered by vacuum filtration to recover a liquid containing bisphenol A.

[0144] (3-1. Purification-distillation step) After that, 23 mol of water was added to the organic layer, whose pH had been lowered to less than 6, and then low-temperature distillation was performed by reducing the pressure from 250 mbar, 20-30°C to 30 mbar, 30°C to recover the by-products diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the methylene chloride, methanol, ethanol, and water used above.

[0145] (3-2. Purification-Washing Step) When the distillation was carried out for a certain period of time according to the above process, bisphenol-A was precipitated to form a slurry state, and the solid was collected by vacuum filtration, and then washed with 3 mol methylene chloride (MC) at 20-30°C for the first time, and washed with 23 mol water at 50°C for the second time.

[0146] (4-1. Further purification step-redissolution step) The washed material was redissolved in 16.6 mol of ethanol.

[0147] (4-2. Additional purification step-adsorption step) After that, lignite activated carbon was added in a ratio of 50% by weight to the waste polycarbonate, and purified by adsorption for 3 hours, and then filtered to remove the lignite activated carbon.

[0148] (4-3. Additional purification step-recrystallization step) Then, 260 mol of water was slowly added to crystallize bisphenol A, and the resulting slurry was vacuum filtered at 20-30° C. to recover bisphenol A (BPA) crystals.

[0149] (5. Drying step) Then, the mixture was dried in a vacuum convection oven at 40° C. to produce a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0150] Example 2 As shown in Table 1 below, a recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the molar ratio of ethanol:methanol:methylene chloride was changed to 9:2:17.

[0151] Example 3 As shown in Table 1 below, a recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the molar ratio of ethanol:methanol:methylene chloride was changed to 8:3:17.

[0152] Example 4 As shown in Table 1 below, a recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the molar ratio of ethanol:methanol:methylene chloride was changed to 7:4:17.

[0153] Example 5 As shown in Table 1 below, a recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the molar ratio of ethanol:methanol:methylene chloride was changed to 6:5:17.

[0154] <Comparative Example: Production of Recycled Bisphenol A Monomer Composition> Comparative Example 1 As shown in Table 1 below, a recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the molar ratio of ethanol:methanol:methylene chloride was changed to 0:11:17.

[0155] Comparative Example 2 As shown in Table 1 below, a recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the molar ratio of ethanol:methanol:methylene chloride was changed to 11:0:17.

[0156] <Experimental Example> The physical properties of the recycled bisphenol A monomer compositions or by-products obtained in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1.

[0157] 1. Purity The recycled bisphenol A monomer composition was dissolved in acetonitrile (ACN) solvent at 1 w% under normal pressure and 20 to 30°C, and the purity of bisphenol A (BPA) was analyzed using UPLC (ultra performance liquid chromatography) on a Waters HPLC system using an ACQUITY UPLC (registered trademark) BEH C18 1.7 μm (2.1 * 50 mm column).

[0158] 2. Color coordinates (L*, a*, b*) The recycled bisphenol A monomer composition was analyzed using a HunterLab UltraScan PRO Spectrophotometer instrument in reflectance mode.

[0159] 3. By-product (DMC, DEC, EMC) content A 1 ml sample of the mixture of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) by-products containing MC, MeOH, EtOH, and water separated in the distillation step was collected and analyzed by gas chromatography (GC) under the following conditions.

[0160] <Gas chromatography (GC) conditions> a)Column:HP-1(L:30m, ID:0.32mm, film:1.05m) b) Injection volume: 1 μl c) Inlet Temp.:260℃, Pressure:6.92psi, Total flow:64.2ml / min, Split flow:60ml / min, Spit ratio:50:1 d) Column flow: 1.2 ml / min e)Oven temp.:70℃ / 3min-10℃ / min-280℃ / 41min(Total 65min) f)Detector Temp.:280℃, H2:35ml / min, Air:300ml / min, He:20ml / min g) GC Model: Agilent 7890 Then, standard samples of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were dissolved in EtOH solvent at the same concentration and the peak area values ​​measured by GC were used as the reference values, and the ratio of the peak area values ​​of each of the carbonate by-products in the sample (diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC)) (peak area value of sample / peak area value of standard sample) was calculated.

[0161] The relative ratio of each carbonate by-product (diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC)) obtained from the GC results was calculated based on the total peak area ratio of 100%, and is shown in Table 1.

[0162] [Table 1]

[0163] As shown in Table 1 above, the recycled bisphenol A monomer compositions obtained in Examples 1 to 5 exhibited high purities of 99.1% to 99.4%. In addition, the recycled bisphenol A monomer compositions obtained in Examples 1 to 5 exhibited color coordinates L* of 95.9 to 96.3, a* of -0.04 to 0.09, and b* of 1.49 to 1.80, and exhibited excellent optical properties. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 to 5 produced all three types of carbonates, namely diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), as by-products. On the other hand, the recycled bisphenol A monomer composition obtained in Comparative Example 2 had a purity of 99.0%, which was reduced compared to the Examples. In addition, the recycled bisphenol A monomer composition obtained in Comparative Example 1 exhibited a color coordinate L* of 95.77, a* of -0.08, and b* of 1.51, while the recycled bisphenol A monomer composition obtained in Comparative Example 2 exhibited a color coordinate a* of 0.11, showing poor optical properties compared to the Examples. Furthermore, only dimethyl carbonate (DMC) was obtained as a by-product of the recycled bisphenol A monomer composition obtained in Comparative Example 1, and only diethyl carbonate (DEC) was obtained as a by-product of the recycled bisphenol A monomer composition obtained in Comparative Example 2.

Claims

1. A step of depolymerizing a polycarbonate-based resin in a solvent containing methanol and ethanol; and separating a carbonate precursor from the depolymerization reaction product, The total amount of methanol and ethanol is 10 to 15 moles per mole of the polycarbonate resin.

2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the ethanol is used in an amount of 1 to 15 moles per mole of the methanol.

3. The depolymerization reaction of the polycarbonate resin is 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the reaction is carried out by reacting the polycarbonate resin with a base in an amount of 0.5 mol or less per mol of the polycarbonate resin.

4. The solvent may be, in addition to methanol and ethanol, 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and dipropyl carbonate.

5. The method for producing a monomer composition for synthesizing recycled plastics according to claim 4, wherein the amount of the organic solvent is 16 to 20 moles per mole of the polycarbonate resin.

6. The method for producing a monomer composition for synthesizing recycled plastics according to claim 4, wherein the amount of the organic solvent is 1.5 to 2 moles per mole of the total of methanol and ethanol.

7. The step of depolymerizing the polycarbonate-based resin in a solvent containing methanol and ethanol includes: preparing a catalyst solution by adding a base to a mixed solvent of methanol, ethanol, and an organic solvent other than methanol and ethanol; 2. The method of claim 1, further comprising the step of adding a carbonate-based resin to the catalyst solution and stirring the mixture.

8. separating a carbonate precursor from the depolymerization reaction product, The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising a step of vacuum distillation of the depolymerization reaction product.

9. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising a purification step of the depolymerization reaction product from which the carbonate precursor has been separated.

10. prior to the step of separating the carbonate precursor from the depolymerization reaction product, 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising a step of neutralizing the depolymerization reaction product with an acid.

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